Fig. 1. Elevated dietary salt intake increases the number of mitochondria-rich cells and Na⁺/K⁺-ATPase activity in trout gill. (A,B) Representative images depicting Na⁺/K⁺-ATPase (NKA) immunofluorescence (red, arrows) in gill sections from (A) control and (B) salt-fed fish; nuclei are stained blue. (C) Morphometric analysis (N=6 for each group) demonstrated a significant increase (P=0.006) in the fractional surface area of mitochondria-rich (NKA immunopositive) cells in the salt-fed (filled bars) fish. (D) Branchial NKA activity (N=10 for each group) was increased threefold (P=0.011) by salt feeding (filled bars). Scale bars, 10 µm. Asterisks in C and D indicate statistically significant difference from control values.